The present invention relates to polymer particles, in particular porous polymeric particles having an aligned pore structure which are useful, e.g., as packing materials for liquid chromatography, particles for porous ink jet receiving layers, electrophotographic toners, adsorbents, cosmetics, paints, building materials, controlled release devices, pharmaceuticals, and the like.
Porous polymer particles are useful for oral, injectable and implantable devices because they have a long circulation time in the body and are efficient drug, enzyme, and protein carriers enabling controlled release of such compositions. The particles form a porous network capable of retaining large amounts of inert and active substances. Such controlled release delivery systems for drugs have a wide variety of advantages over conventional forms of drug administration. Some of these advantages include: decreasing or eliminating the oscillating drug concentrations found with multiple drug administrations; allowing the possibility of localized delivery of the drug to a desired part of the body; preserving the efficacy of fragile drugs; reducing the need for patient follow-up care; increasing patient comfort and improving patient compliance.
Porous polymer particles used for drug delivery, e.g. through an intravascular pathway, must be small in size in order to circulate in the body. A problem with prior art particles is that although small in median size, the quality of the particle size distribution may be inadequate. In particular, there may be a tail of larger particles in the particle size distribution which can give a gritty feel during oral administration, plug needles used for injection, or inhibit circulation in the body. Extensive and tedious filtration may be required in order to remove these larger particles. On the other hand, there may also be significant fractions of fine particles in the particle size distribution which can lead to inadequate loading of drug and also the subsequent release profiles of loaded drugs.
Another problem with prior art particles is that some porous polymer particles may be stabilized by small surfactant molecules or by water-soluble polymers. These prior art stabilizers or emulsifiers are sometimes not desired because they may be toxic or create surface properties on the porous polymer particle which are inappropriate for the application.
Porous polymer particles are also useful for ink jet receivers. While a wide variety of different types of image-recording elements for use with ink jet devices have been proposed heretofore, there are many unsolved problems in the art and many deficiencies in the known products which have limited their commercial usefulness. One such problem is that larger than desired particles create visible defects.
Porous particles containing colorants are useful as electrophotographic toners. U.S. Pat. Nos. 7,887,984 and 7,754,409 describe porous toner particles prepared by a multiple-emulsion—evaporation method. Such a process involves the preparation of a first water-in-oil (W1/O) emulsion, which is then dispersed into a second water phase to form a water-in-oil-in-water (W1/O/W2) emulsion, from which the solvent in the oil phase (O) is removed and porous particles obtained. The porous particles obtained contain discrete pores formed as a result of the W1 phase droplets, and the pores thus have substantially spherical, non-aligned shapes.
Porous polymer particles may also be prepared with spray drying or spray freeze-drying techniques. Spray drying of a polymer solution sometimes leads to the formation of porous particles even when no particular porogens are used. However, spray freezing followed by freeze-drying produces pores in the resulting particles due to temperature induced phase separation. When the solvent used to make the polymer solution can freeze to form shaped crystals, aligned pores may form inside the particles after freeze-drying. For example, in US Patent Application Pub. No. 2011/0262654A1, a spray freezing and freeze-drying process was disclosed for the preparation of porous polymer particles encapsulating metallic flakes. The use of some high melting organic solvents leads to the formation of aligned pores after removal of the frozen solvent. In general, the particle size and particle size distribution are controlled by the spraying step (atomization step), and a relatively wide particle size distribution is expected.
Freeze drying of specific oil-in-water emulsions was shown to produce particles with aligned porosity (Adv. Funct. Mater. 2008, 18, 222-228). Polymer solutions in o-xylene (or cyclohexane) were emulsified with water at a controlled rate of shearing in the presence of a surfactant and a water soluble polymer (such as PVA). The emulsion was then freeze-dried and porous particles with aligned pores could be obtained. However, the particle size in this method is believed to be controlled mainly by the shearing during the emulsification step, and the particle size distribution is thus expected to be relatively broad.
There is a need to easily prepare particles with aligned pores and narrow particle size distribution. Uniform particles generally have advantages over polydisperse particles in many applications such as drug encapsulation and delivery. Thus porous particles with aligned pores and with narrow particle size distribution are desired.